EP2437075A1 - Ortung von Teilentladungen in Stromkabeln - Google Patents

Ortung von Teilentladungen in Stromkabeln Download PDF

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Publication number
EP2437075A1
EP2437075A1 EP11183316A EP11183316A EP2437075A1 EP 2437075 A1 EP2437075 A1 EP 2437075A1 EP 11183316 A EP11183316 A EP 11183316A EP 11183316 A EP11183316 A EP 11183316A EP 2437075 A1 EP2437075 A1 EP 2437075A1
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EP
European Patent Office
Prior art keywords
power cable
location
pulse
partial discharge
detecting
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Granted
Application number
EP11183316A
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English (en)
French (fr)
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EP2437075B1 (de
Inventor
Antonius Jacobus Paulus Jansen
Hans Fijlstra
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Locamation BV
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Locamation BV
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Publication of EP2437075B1 publication Critical patent/EP2437075B1/de
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • G01R31/1227Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
    • G01R31/1263Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
    • G01R31/1272Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/11Locating faults in cables, transmission lines, or networks using pulse reflection methods

Definitions

  • the present invention relates to an on-line measurement method for detection of a location of a partial discharge in a power cable that is in use during normal operation, the power cable having a conductor, a dielectric around the conductor and a conductive earth sheet arranged around the dielectric.
  • the present invention relates to an on-line measurement system for detection of a location of a partial discharge in a power cable.
  • European patent application EP-A-1 516 194 discloses a method and system for transmitting an information signal over a power cable. This is used e.g. for on-line measurement of the location of a partial discharge in the power cable.
  • the measurement consists of the power cable under test, whereon two measurement units are connected. They both have a connection to a central processing unit, for example using a wired connection.
  • the data from the two measurement units is registered and compared to localize the PD.
  • the measurement set-up requires two measurement units and two data connections to a central processing unit.
  • a source 10 is used to generate AC signals for the measurements, with a suitably high level in order to cause partial discharges in the cable.
  • the present invention seeks to provide a more cost-effective measurement for power cables, e.g. to detect possible defects in the power cable in an early stage using partial discharge detection.
  • the prior art system using on-line measurement as discussed above has the disadvantage that two active units are required, which is expensive with regard to placement, set/up costs and maintenance. Furthermore, reliability may be an issue, as if one of the two active units fails the systems stops working. Also, the system needs time synchronization between the two units, which results in a lower accuracy as the time syncing can cause erroneous measurements. Finally, the required communication between the two active units may cause data errors.
  • a method according to the preamble defined above comprises providing a master measuring unit at a first location along the power cable, and during normal operation of the power cable wherein the power cable is connected to a power grid:
  • the present method allows to perform an on-line measurement of a power cable, i.e. during operation of the power cable while a high voltage is present.
  • the power cable can be tested while being live, i.e. part of the utility grid, and can be electrically connected at one or both ends to parts of the power grid under voltage. Only a single measurement unit is needed, as a result of which the measurement is more cost-effective, and more reliable (no synchronization needed).
  • the impedance change is provided by a passive element in the electrical circuit of the power cable.
  • a passive element is more cost-effective than having to use two active units for performing a measurement.
  • the passive element is a coupling of the power cable to a further electrical element, such as a transformer.
  • the passive element is provided as an additional element, such as an element of a low magnetic resistance.
  • the additional element is e.g. a ferrite element such as a ferrite core.
  • the ferrite core can be positioned at the second location (which may be easily accessible for measurement personnel), and is e.g. positioned around a ground lead connected to the conductive earth sheet (which is usually present in e.g. a substation).
  • the ferrite core can be positioned around an unshielded part of the conductor, or in an even further embodiment, around an extended conductive ground sheet of the power cable, downstream from a ground lead connected to the conductive earth sheet.
  • the method further comprises determining an out and return distance (i.e. (2x + 2y)*s taking the parameters mentioned above) between the first location (master measuring unit) and the second location (passive element or slave unit), and using the out and return distance to determine the distance between the first location and the location of the partial discharge. As the measurement is performed from the first location by the master measuring unit, this may provide a more useful indication of where along the power cable a partial discharge has occurred.
  • Determining the out and return distance in a further embodiment comprises injecting a distance measuring signal at the first location, and detecting an associated reflected pulse. Detection of the associated reflected pulse can be enhanced by using knowledge of the characteristics of the distance measuring signal, such as (pulse) shape, modulation, chirp, etc.
  • the out and return distance may be provided in another manner, e.g. by measuring (or estimating) the physical distance between the first and second location, or by looking up this distance in an administrative system of the cable owner.
  • the detection measurements of the direct pulse, and especially of the reflected pulse may provide difficult in a noisy environment, as usually encountered in power cable systems. To allow robust and accurate pulse detection, several measures can be taken as mentioned in the following embodiments.
  • the method further comprises detecting the direct pulse (and possibly also the reflected pulse) by using a predetermined detection threshold value.
  • the method further comprises detecting the direct pulse (and possibly also the reflected pulse) by using time-frequency analysis of peaks.
  • prior knowledge may be used, e.g. that the pulse caused by a partial discharge will occur at the main frequency of the AC signal on the power cable, or a fraction thereof (e.g. 50/n Hz, n being an integer number). Further improvement may be obtained when using multiple (synchronized) occurrences of partial discharges, e.g. by adding up multiple signal periods in time (e.g. at least 10 time period signals, or even more than 100 time period signals).
  • detecting the direct pulse and the reflected pulse is implemented using correlation techniques.
  • correlation techniques may be advantageously used to detect the reflected signal, even when in a noisy environment.
  • the method further comprises using a reverse transformation of the direct pulse signal shape using a dispersion characteristic of the power cable, in order to detect the reflected pulse.
  • the pulse caused by a partial discharge in a power cable is initially very high in high frequency content, but dispersion in the power cable will cause the pulse to spread out in the frequency domain. Reverse transformation may then aid in restoring the original pulse shape and obtain a more robust and accurate correlation match.
  • a further aspect of the present invention relates to an on-line measurement system for detection of a location of a partial discharge in a power cable having a conductor, a dielectric around the conductor and a conductive earth sheet arranged around the dielectric, the on-line measurement system comprising a master measuring unit interfacing with the power cable at a first location, the master measuring unit being arranged to execute the method according to any one of the present method embodiments.
  • the on-line measurement system further comprises a passive element, which in operation is provided at the second location along the power cable.
  • the passive element is e.g. a ferrite element (ferrite core) which can be positioned around the power cable at the second location.
  • Power grids need maintenance after their initial installment.
  • One threat to power grids is partial discharges (also indicated as PD), which can cause a breakdown if the power cable is not repaired in time. Since most of the medium voltage network in e.g. the Netherlands is underground, detecting these partial discharges without visually checking the cable is important. Measuring partial discharges has been possible for some time now, but the invention presented in this document simplifies that measurement and offers many improvements over prior art methods and systems.
  • a PD is visible as a pulse Pd, it causes a short lasting surge of power and lower voltage over the core 2 of the power cable 1.
  • the complement pulse Pd' caused by the temporary, short lasting power gain and voltage rise, passes over the conductive earth sheath 4.
  • a pulse of 1 A is visible up to about 6 kilometers. If the core 2 and the conductive earth sheath 4 are measured together, no pulse is seen as the positive and negative voltage oscillations neutralize each other. By measuring either one, the pulse Pd can be detected.
  • a PD is in fact a tiny spark inside the power cable 1. They occur in damaged, eroded or flawed parts of the dielectric 3. With each discharge, minute damage is done to the dielectric 3. This implies a deterioration of the power cable 1 over time, due to the occurrence of partial discharges. If a weak spot causing PDs goes undetected, an electrical breakdown will take place. The negative effects of such a breakdown in a power cable 1 are obvious, costly and should be avoided if possible. Electrical companies will go to great lengths to prevent any breakdown in the power grid, and continuously monitor the condition of their network.
  • the present invention embodiments as described below simplify the measurement of partial discharges in power cables 1 during normal operation of the power cable 1, i.e. when one or both ends of the power cable 1 are electrically connected to the power grid. Partial discharges can damage the power cable 1, and early detection can prevent a breakdown. Current detection methods use two active units on either side of the subject cable, which both measure pulses from a partial discharge occurring on the subject stretch of cable. The present invention embodiments use only one active unit and a passive slave mirror, which reflects the partial discharge pulse. This offers many advantages over the previous system.
  • FIG. 1 shows a simplified image of the use of the present invention embodiments.
  • the power cable 1 to be tested comprises a conductor 2, a dielectric 3 around the conductor 2 and a conductive earth sheet 4 arranged around the dielectric 3.
  • the power cable 1 could comprise multiple conductors 2.
  • the power cable 1 is connected to a further power cable 7 using a coupling 5.
  • a separate ground cable 6 is used connected to the earth sheet 4 of the power cables 1 and 7 and to ground as indicated.
  • a master measuring unit 10 is provided around the power cable 1 at a first location, and interfaces with the power cable to allow measurement of electrical signals (voltage based and/or current based).
  • the master measuring unit 10 may be connected to a processing system 12 for processing of the measured signals.
  • the connection may be directly or using wireless connections.
  • the master measuring unit 10 may be integrated with a processing system 12.
  • the master measuring unit 10 and the processing system 12 are arranged to implement the method embodiments of the present invention.
  • the on-line measurement system 10-12 measures partial discharges in medium voltage power cables 1 and comprises one active master measuring unit 10 and one passive slave unit (passive element) 11.
  • the master measuring unit 10 is capable of measuring PD pulses (and in a further embodiment for sending out simple energy pulses), and communicating with a central computer 12.
  • the slave unit 11 in this embodiment is a ferrite core positioned at a second location which locally increases the impedance of the power cable 1 from 11 to about 100 ohms.
  • the passive slave 11 acts as a mirror and causes a part of the PD pulse to reflect (indicated as Pr in Fig. 1 ).
  • the use of only one active unit reduces costs of the measurement system. It also saves on maintenance and installation and reduces the risk of a breakdown.
  • the set up is also easier, as the installation of a slave unit 11 requires less effort than a master unit 10.
  • the use of a master/slave combination as in the present invention embodiments has no need for communication (between two active units over the power cable as in prior art systems). No information signal is being sent and received, and synchronizing between two units is not necessary. When there is no time synchronization, there can also be no time error. Any corrected measurement is less accurate than a measurement that needs no correction.
  • a PD occurs somewhere along the power cable 1 (indicated by the reference numeral 15 in Fig. 2 ) and sends out a pulse in both directions of the power cable 1, i.e. travels a distance x*s to the master measuring unit 10, and a distance y*s to the slave unit 11.
  • the pulse initially arrives at the master measuring unit 10 or slave unit 11, and then a certain time later at the other position.
  • the signal Pd arrives at the master measuring unit 10, it is recorded.
  • the signal Pr arrives at the slave unit 11, it is reflected towards the master measuring unit 10, where it arrives some time later, being recorded as well.
  • the master measuring unit 10 records not one but two pulses (Pd and Pr, see Fig. 1 ).
  • the first and stronger pulse Pd comes directly from the PD, the second and weaker pulse Pr is reflected by the slave unit 11.
  • the exact location of the PD can be determined.
  • the time for signal to travel from PD to master measuring unit 10 is equal to x
  • the time for signal to travel from PD to slave unit 11 is equal to y.
  • the time distance between the first location (master measuring unit 10) and second location (slave unit 11) is equal to x+y.
  • the first signal (Pd) arrives after x
  • the second signal (reflection, Pr) arrives after 2y + x.
  • the time difference is then equal to 2y.
  • the traveling speed of the signal can be assumed known (i.e. is a characteristic of the power cable 1) and is equal to s.
  • the distance between the location of the PD and the second location (slave unit) is then equal to y*s.
  • the present method embodiments comprise determining the location of a partial discharge in the power cable 1 during normal operation of the power cable 1, wherein the power cable is connected to a power grid, by providing a master measuring unit 10 at a first location along the power cable 1. Determining the location comprises:
  • the impedance change is provided by a passive element 11 in the electrical circuit of the power cable 1.
  • a reflection may already be caused by a coupling of the power cable 1 to a further cable element (e.g. a transformer).
  • a more practical and more reliable source of an impedance change in the electrical circuit of the power cable 1 is to use an element of a low magnetic resistance, such as a ferrite element 11 as discussed above.
  • the ferrite element 11 can be a ferrite core of a size sufficient to encircle an element of the electrical circuit. Possible locations of the ferrite core as reflecting passive element 11 are shown in the partial view shown in Fig. 3 .
  • the ferrite core 11 may be provided at location A (around the ground lead 6 connected to the conductive earth sheet 4), location B (an unshielded part of the conductor 2) or location C (an extended part of the conductive ground sheet 4 of the power cable 1, downstream from a ground lead 6 connection to the conductive earth sheet 4.
  • Locations A and C have the benefit that no voltage carrying parts of the electrical circuit need to be handled to position the passive element, which provides benefits in view of safety.
  • Location C has the benefit that the reflected pulse Pr will suffer less from a noisy environment.
  • the method comprises determining an out and return distance ((2x + 2y)*s) between the first location (master measuring unit 10) and the second location (slave unit 11), and using the out and return distance to determine the distance x between the first location and the location of the partial discharge.
  • determining the out and return distance may comprise injecting a distance measuring signal at the first location, and detecting an associated reflected pulse.
  • a pulse is sent from the first position (by master measuring unit 10) to the slave mirror 11, where the signal is reflected, and then the signal is returned towards the first position where it is received.
  • the master measuring unit 10 sends and receives the same pulse.
  • the time between sending and receiving (2x+2y, see Fig. 2 ) is double the time needed for the signal to travel the length of power cable 1 subj ect to measurement.
  • the exact distance (x+y)*s between the master measuring unit 10 and the slave unit 11 can be determined.
  • the reflected signal may be identified using specific characteristics of the signal, such as (pulse) shape, modulation of the signal, chirp, etc.
  • Alternative methods for determining the out and return distance may be to measure (or estimate) the physical distance between the first and second location.
  • a further alternative would be to look up the distance in an administrative system of the grid owner.
  • Noise is the fundamental limitation to the range over which electrical signals can be transmitted and received.
  • noise limits the distance between the master measuring unit 10 and the slave unit 11, or it limits the sensitivity of the measurement.
  • the maximum measuring distance is limited by noise as well.
  • Pr reflected signal Pr
  • the measuring distance is halved. On average, a signal is measurable up to 6 km, with reflection this means a measuring range of only 3 km. Noise would lower the measuring range of the product. There is a solution to this disadvantage when compared to prior art.
  • the air bubble in the dielectric 3 in which it occurs is relatively small.
  • the pulse Pd may be below the noise level on the power cable 1, due to circumstances as interference from other electrical systems nearby or environmental conditions of the power cable 1. With regular techniques, the PD signal cannot be discerned from the noise that is measured.
  • a simple threshold method is used: the method further comprises detecting the direct pulse (and possibly also the reflected pulse) by using a predetermined detection threshold value. Once the direct pulse Pd has been detected (and e.g. its shape is known) further signal analysis techniques may be used to detect the reflected pulse Pr, even when in a noisy environment.
  • the method further comprises detecting the direct pulse (and possibly also the reflected pulse) by using time-frequency analysis.
  • the knowledge that partial discharges occur at weak spots implies that partial discharges will occur at a frequency of f 0 /n Hz (f 0 being the normal operating frequency of the power cable, e.g. 50 Hz, and n being an integer number), possibly not at every cycle of the power signal, but at least at similar intervals thereof. This opens the opportunity to analyse longer time periods of signals, and provide an improvement in noise cancellation by using at least 10, e.g. 100 PD occurrences.
  • detecting the direct pulse and the reflected pulse is implemented using correlation techniques.
  • the direct pulse Pd and reflected pulse Pr travel in the same type of power cable 1, the shapes of the pulses will be similar, which allows the use of correlation techniques.
  • this method may be even further refined, e.g. using a reverse transformation of the direct pulse signal shape using a dispersion characteristic of the power cable 1.
  • noise mitigation embodiments allow to measure below the noise level.
  • Noise is irregular and erratic, and by adding up these signals, they should level out.
  • a PD signal however is neither irregular nor erratic, and occurs with a certain, not necessarily constant, time interval (related to the 50 Hz power signal).
  • Fig. 4 gives a simplified image of this process. It is only an example of the workings and in no way an exact representation of a real measurement.
  • the signals 1, 2, 3 and 4 in Fig. 4 present different measurements synchronized over a certain stretch of time. For simplified representation, only 4 signals are drawn. In real measurement, 100 signals or more could be used. By adding up, the noise levels out, but the PD sticks out. In the signals 1, 2, 3 and 4, no clear spike of a PD is visible. The S line, is the final result after filtering and clearly shows the PD signal. This technique can significantly improve on the range and sensitivity of the system.
  • PD measurement in medium voltage power cables 1 is the initial intended application for the present invention embodiments.
  • Single sided measurement and data processing is not limited to this purpose alone. In the future, it may be used as a means of cable diagnostic system.
  • a PD does affect cable quality, but is not the only factor that does, nor the only evidence a cable might break or a power network might fail. Other sources of failure may be detected using the present invention embodiments as well.
  • the intention of every application of this invention is to locate any weak spot prior to failure or repair; to prevent breakdown of the subject power cable network.
  • the boundaries of the presented system are electrical wired systems, using conductive cables; it is not applicable to wireless or optical systems.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Testing Relating To Insulation (AREA)
  • Locating Faults (AREA)
EP11183316.6A 2010-10-01 2011-09-29 Ortung von Teilentladungen in Stromkabeln Active EP2437075B1 (de)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL2005431A NL2005431C2 (en) 2010-10-01 2010-10-01 Method and system for on-line measurement in power cables.

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EP2437075A1 true EP2437075A1 (de) 2012-04-04
EP2437075B1 EP2437075B1 (de) 2014-03-05

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104655995A (zh) * 2015-01-29 2015-05-27 国家电网公司 一种电力电缆局放源双端定位方法
CN105021961A (zh) * 2015-07-10 2015-11-04 西安交通大学 一种架空绝缘线局部放电检测及定位装置及方法
CN105093083A (zh) * 2015-08-31 2015-11-25 广州供电局有限公司 电缆局部放电信号定位装置以及定位方法
EP3106888A1 (de) 2015-06-15 2016-12-21 Seitz Instruments AG Verfahren und system zur teilentladungsmessung an einem stromkabel
WO2019177749A1 (en) * 2018-03-15 2019-09-19 Rosemount Inc. Elimination of floating potential when mounting wireless sensors to insulated conductors
US10833531B2 (en) 2018-10-02 2020-11-10 Rosemount Inc. Electric power generation or distribution asset monitoring
CN111929553A (zh) * 2020-10-19 2020-11-13 四川大学 一种基于相速度频变特性的局部放电定位方法
US11067639B2 (en) 2017-11-03 2021-07-20 Rosemount Inc. Trending functions for predicting the health of electric power assets
US11181570B2 (en) 2018-06-15 2021-11-23 Rosemount Inc. Partial discharge synthesizer
US11313895B2 (en) 2019-09-24 2022-04-26 Rosemount Inc. Antenna connectivity with shielded twisted pair cable
US11448682B2 (en) 2017-03-02 2022-09-20 Rosemount Inc. Trending functions for partial discharge
JP7475740B1 (ja) 2023-03-14 2024-04-30 四日市電機株式会社 部分放電検出システム

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US11177055B2 (en) 2017-03-06 2021-11-16 Savannah River Nuclear Solutions, Llc Leading/lagging cable referencing platform for monitoring the health of underground cable networks
CN111289861B (zh) * 2020-03-26 2022-01-25 云南电网有限责任公司电力科学研究院 一种局部放电源位置的检测方法

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EP1516194A2 (de) 2002-06-21 2005-03-23 Stichting Voor De Technische Wetenschappen Verfahren und system zur übermittlung eines informationssignals über ein stromleitungskabel

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DE947497C (de) * 1953-05-30 1956-08-16 Telefunken Gmbh Anordnung zur quantitativen Bestimmung von Inhomogenitaeten in Breitbandkabeln nach dem Impulsverfahren
US3991364A (en) 1974-01-30 1976-11-09 Kabel-Und Metallwerke Gutehoffnungshutte Aktiengesellschaft Autocorrelation method for detecting insulation defects in cable
US5767684A (en) 1992-11-05 1998-06-16 N.V. Kema Method and apparatus for measuring partial discharges in cables
US5369366A (en) * 1993-02-12 1994-11-29 Cable Repair Systems Corporation Method of finding faults in a branched electrical distribution circuit
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EP1516194A2 (de) 2002-06-21 2005-03-23 Stichting Voor De Technische Wetenschappen Verfahren und system zur übermittlung eines informationssignals über ein stromleitungskabel

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104655995A (zh) * 2015-01-29 2015-05-27 国家电网公司 一种电力电缆局放源双端定位方法
EP3106888A1 (de) 2015-06-15 2016-12-21 Seitz Instruments AG Verfahren und system zur teilentladungsmessung an einem stromkabel
CN105021961A (zh) * 2015-07-10 2015-11-04 西安交通大学 一种架空绝缘线局部放电检测及定位装置及方法
CN105021961B (zh) * 2015-07-10 2018-12-07 西安交通大学 一种架空绝缘线局部放电检测及定位装置及方法
CN105093083A (zh) * 2015-08-31 2015-11-25 广州供电局有限公司 电缆局部放电信号定位装置以及定位方法
US11448682B2 (en) 2017-03-02 2022-09-20 Rosemount Inc. Trending functions for partial discharge
US11067639B2 (en) 2017-11-03 2021-07-20 Rosemount Inc. Trending functions for predicting the health of electric power assets
US10794736B2 (en) 2018-03-15 2020-10-06 Rosemount Inc. Elimination of floating potential when mounting wireless sensors to insulated conductors
WO2019177749A1 (en) * 2018-03-15 2019-09-19 Rosemount Inc. Elimination of floating potential when mounting wireless sensors to insulated conductors
US11181570B2 (en) 2018-06-15 2021-11-23 Rosemount Inc. Partial discharge synthesizer
US10833531B2 (en) 2018-10-02 2020-11-10 Rosemount Inc. Electric power generation or distribution asset monitoring
US11313895B2 (en) 2019-09-24 2022-04-26 Rosemount Inc. Antenna connectivity with shielded twisted pair cable
CN111929553A (zh) * 2020-10-19 2020-11-13 四川大学 一种基于相速度频变特性的局部放电定位方法
JP7475740B1 (ja) 2023-03-14 2024-04-30 四日市電機株式会社 部分放電検出システム

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EP2437075B1 (de) 2014-03-05

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